Recovering Ethanol with Sidestreams to Regulate C3+ Alcohols Concentrations

ABSTRACT

This invention relates to purification and/or recovery of ethanol from a crude ethanol product obtained from the hydrogenation of acetic acid. Separation and purification processes of a crude ethanol mixture are employed to allow recovery of ethanol and remove impurities. In particular, the process involves one or more sidestreams to regulate C 3 + alcohols concentration in the recovered ethanol.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.13/292,885, filed on Nov. 9, 2011, which claims priority to U.S.application Ser. No. 13/094,588, filed on Apr. 26, 2011, and U.S.application Ser. No. 13/094,657, filed on Apr. 26, 2011, the entirecontents and disclosures of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to processes for producing andrecovering ethanol and, in particular, to processes for recoveringethanol from a crude product from acetic acid hydrogenation thatcontains C₃+ alcohols, e.g., heavy alcohols.

BACKGROUND OF THE INVENTION

Ethanol for industrial use is conventionally produced from petrochemicalfeed stocks, such as oil, natural gas, or coal, from feed stockintermediates, such as syngas, or from starchy materials or cellulosematerials, such as corn or sugar cane. Conventional methods forproducing ethanol from petrochemical feed stocks, as well as fromcellulose materials, include the acid-catalyzed hydration of ethylene,methanol homologation, direct alcohol synthesis, and Fischer-Tropschsynthesis. Instability in petrochemical feed stock prices contributes tofluctuations in the cost of conventionally produced ethanol, making theneed for alternative sources of ethanol production all the greater whenfeed stock prices rise. Starchy materials, as well as cellulosematerial, are converted to ethanol by fermentation. However,fermentation is typically used for consumer production of ethanol, whichis suitable for fuels or human consumption. In addition, fermentation ofstarchy or cellulose materials competes with food sources and placesrestraints on the amount of ethanol that can be produced for industrialuse.

Ethanol production via the reduction of alkanoic acids and/or othercarbonyl group-containing compounds has been widely studied, and avariety of combinations of catalysts, supports, and operating conditionshave been mentioned in the literature. During the reduction of alkanoicacids, e.g., acetic acid, other compounds are formed with ethanol or areformed in side reactions. These impurities limit the production andrecovery of ethanol from such reaction mixtures. For example, duringhydrogenation, esters are produced that together with ethanol and/orwater form azeotropes, which are difficult to separate. In addition,when conversion is incomplete, acid remains in the crude ethanolproduct, which must be removed to recover ethanol.

EP02060553 describes a process for converting hydrocarbons to ethanolinvolving converting the hydrocarbons to ethanoic acid and hydrogenatingthe ethanoic acid to ethanol. The stream from the hydrogenation reactoris separated to obtain an ethanol stream and a stream of acetic acid andethyl acetate, which is recycled to the hydrogenation reactor.

U.S. Pat. No. 2,801,209 describes production of ethanol from olefindehydration that uses sidestreams to remove oils that buildup in thecolumns while recovering ethanol.

Therefore, a need remains for improving the recovery of ethanol from acrude product obtained by reducing alkanoic acids, such as acetic acid,and/or other carbonyl group-containing compounds.

SUMMARY OF THE INVENTION

In a first embodiment, the present invention is directed to a processfor producing ethanol, comprising hydrogenating acetic acid in a reactorin the presence of a catalyst to form a crude ethanol product,separating at least a portion of the crude ethanol product in a firstdistillation column to yield a first residue comprising acetic acid andwater, wherein a substantial portion of the water in the crude ethanolproduct that is fed to the column is removed in the first residue, afirst distillate comprising ethanol, ethyl acetate and water, and one ormore sidestreams comprising one or more C₃+ alcohols, removing waterfrom at least a portion of the first distillate to yield an ethanolmixture stream comprising less than 10 wt. % water, and recoveringethanol from the ethanol mixture stream.

In a second embodiment, the present invention is directed to a processfor producing ethanol, comprising hydrogenating acetic acid in a reactorin the presence of a catalyst to form a crude ethanol product,separating a portion of the crude ethanol product in a firstdistillation column to yield a first distillate comprising ethyl acetateand a first residue comprising one or more C₂+ alcohols, acetic acid andwater, wherein a majority of ethanol in the crude ethanol product thatis fed to the column is removed in the first residue, separating aportion of the first residue in a second distillation column to yield asecond residue comprising acetic acid and water, a second distillatecomprising ethanol, and one or more sidestreams comprising one or moreC₃+ alcohols.

BRIEF DESCRIPTION OF DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, wherein like numeralsdesignate similar parts.

FIG. 1 is a schematic diagram of an ethanol production system having twocolumns with sidestreams to regulate C₃+ alcohols in the initial columnin accordance with one embodiment of the present invention.

FIG. 2 is a schematic diagram of an ethanol production system having twocolumns with sidestreams to regulate C₃+ alcohols in the last column inaccordance with one embodiment of the present invention.

FIGS. 3 and 4 are graphical simulations illustrating the reduction ofC₃+ alcohols bulging as a result of the addition of sidestreams inaccordance with various embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to processes for recovering ethanolproduced by hydrogenating acetic acid in the presence of a catalyst.There may be additional components present during hydrogenationincluding acids, esters, aldehydes, and anhydrides, depending on theimpurity level of the acetic acid feed. These impurities may be reducedalong with acetic acid to produce C₃+ alcohols, e.g., heavy alcohols. Inaddition, side reactions during acetic acid hydrogenation may result information of C₃+ alcohols. The C₃+ alcohols may be formed in minoramounts, e.g., less than 10 wt. %, that when present are withdrawn withthe recovered ethanol. This may lead to an ethanol product with levelsof C₃+ alcohols impurities that may require further processing. Thefurther processing may be inefficient to remove the minor amounts of theC₃+ alcohols from the ethanol. Although some C₃+ alcohols may betolerated in certain ethanol applications, such as fuel grade ethanol,it is advantageous to regulate the C₃+ alcohols concentration in therecovered ethanol. Embodiments of the present invention overcome theproblems associated with C₃+ alcohols by providing an efficient processto regulate the amount C₃+ alcohols in the recovered ethanol.

In particular, the present invention relates to recovering ethanol inless than two distillation columns so that the C₃+ alcohols do not buildup in multiple columns. In one embodiment, the C₃+ alcohols are removedin the initial separation column via one or more sidestreams. In anotherembodiment, the C₃+ alcohols are initially concentrated in the residuealong with ethanol and then separated via one or more sidestreams. Inone embodiment, the residue comprises from 20 to 95 wt. % C₂+ alcohols,where of those C₂+ alcohols 90% to 99.9% are ethanol and from 0.01% to10% are C₃+ alcohols. In preferred embodiments, the C₂+ alcoholscomposition comprises 95 to 99.9 wt. % ethanol and 0.01 to 5 wt. % C₃+alcohols.

Higher alcohols such as C₃+ alcohols may be expected to be formed due tohigher acids and/or esters in the feed. However, even in the absence ofhigher acids and/or esters, higher alcohols may be formed due to sidereactions when hydrogenating acetic acid. These side reactions createcapacity and purification inefficiencies in the separation system andmay build up to unacceptable levels in the finished ethanol composition.The embodiments of the present invention advantageously reduce the C₃+alcohol concentration in the finished ethanol composition.

C₂+ alcohols include ethanol and C₃+ alcohols. For purposes of thepresent invention, C₃+ alcohols are generally referred to as heavyalcohols and comprise alcohol species that generally have a higherboiling point than ethanol. These alcohols species may also includeazeotropes of the C₃+ alcohols. The C₃+ alcohols have at least threecarbons, e.g., at least four carbons or at least five carbons. In termsof ranges, C₃+ alcohols include from C₃ to C₆ alcohols, or morepreferably from C₃ to C₅ alcohols. Examples of C₃+ alcohols includeisopropanol, n-propanol, n-butanol, 2-butanol, isobutanol, tert-butanol,2,2-dimethyl-1-propanol, 3-pentanol, 2-pentanol, 1-pentanol,3-methyl-2-butanol, 2-methyl-2-butanol, mixtures thereof, and azeotropesthereof. In one embodiment, the C₃+ alcohols include isopropanol,n-propanol, n-butanol, and/or 2-butanol.

The separation of the crude ethanol product is controlled bythermodynamic phase equilibrium, which provides a concentration gradientthroughout each column such that ethanol may be withdrawn overhead, andwater and acetic acid may exit the bottom. However, when additionalspecies, such as C₃+ alcohols and/or mixtures of C₃+ alcohols and ethylacetate, are present in the column, a concentration gradient sufficientfor separation may not exist, thereby causing the C₃+ alcohols to buildup, e.g., bulge, at particular points within the column. In oneembodiment, sidestreams of C₃+ alcohols may be taken in the liquid orvapor phase. In preferred embodiments, sidestreams are taken atlocations in the column approximate to where the C₃+ alcohols build up.There may be multiple sidestreams to regulate the concentration of C₃+alcohols.

Each of the C₃+ alcohols may build up at different points within thecolumns. In some embodiments, one of the heavy alcohols may build up andthat location is selected for reducing the concentration of C₃+alcohols. In particular 2-butanol or n-butanol may be used to determinewhere to withdraw the sidestreams.

In one embodiment, sidestreams remove the C₃+ alcohols such thatdistillate stream comprises less than 1000 wppm of C₃+ alcohols, e.g.,less than 500 wppm or less than 400 wppm. In terms of ranges, the C₃+alcohols concentration range in the distillate stream may be from 10 to1000 wppm, e.g., from 10 to 500 wppm or from 10 to 400 wppm. Inparticular, the concentration of isopropanol, n-propanol, n-butanol,and/or 2-butanol in distillate stream may be less than 1000 wppm, e.g.,less than 500 wppm or less than 400 wppm.

Optionally, an analyzer (not shown) may be used to measure the C₃+alcohols concentration in the distillate stream and/or residue stream.When the analyzer measures that the concentration of the compositionwithin column exceeds a target or specification level for the particularC₃+ alcohols, a signal may be provided and a sidestream may be takenfrom column to reduce the C₃+ alcohols concentration in the distillateand/or residue stream. For example, a target level of C₃+ alcoholsconcentration may be less than 1000 wppm, e.g., less than 500 wppm, orless than 400 wppm. One or more additional analyzers may also be used tomeasure the C₃+ alcohols concentration throughout the column.

In a first embodiment of the present invention, the process involvesintroducing the crude ethanol product to an initial separation column(first column), which separates the crude ethanol product into adistillate comprising ethanol, ethyl acetate and water, and a residuecomprising water and unreacted acetic acid. One or more sidestreams arewithdrawn from the first column to regulate C₃+ alcohol concentration.Water is then removed from the distillate to form an ethanol mixturestream, preferably comprising less than 10 wt. % water, less than 6 wt.% water or less than 4 wt. % water. In terms of ranges, the ethanolmixture stream comprises from 0.001 to 10 wt. % water, e.g., from 0.01to 6 wt. % water or from 0.1 to 4 wt. % water. Product ethanol is thenrecovered from the ethanol mixture stream. Preferably, removing water inthe distillate of the initial column and reducing the concentration ofC₃+ alcohols may improve overall separation efficiency in recoveringethanol.

Water and ethanol form an azeotrope that is difficult to separate in adistillation column. The ethanol-water azeotrope limits the recoverableethanol in distillation columns to an ethanol product comprising about92-96 wt. % of ethanol. The energy required to approach this azeotropein a distillation column, regardless of the presence of other compounds,is significant. The present invention involves using less energy in theinitial column than would be required to approach the azeotrope,resulting in water being carried overhead in the distillate. Water isthen removed from the distillate using a water separator, whichbeneficially requires less energy than is required for approaching thewater/ethanol azeotrope in a distillation column. Thus, the presentinvention provides a low energy approach for dehydrating a crude ethanolproduct and thus removing water that is co-produced with ethanol.

The concentration of water in the distillate may vary depending on theacetic acid conversion. In one embodiment, the distillate compriseswater in an amount greater than the amount of water in the ethanol/waterazeotrope, e.g., in an amount greater than 4 wt. %, greater than 5 wt.%, or greater than 7 wt. %. In terms of ranges, the distillateoptionally comprises water in an amount from 4 wt. % to 38 wt. %, e.g.,from 7 wt. % to 32 wt. %, or from 7 wt. % to 25 wt. %.

Because the water concentration in the distillate is typically greaterthan the acceptable amount of water for industrial or fuel grade ethanolapplications, in one embodiment of the present invention, the processinvolves removing a substantial portion of the water from the distillateto produce an ethanol mixture. Preferably, the water is removed beforeseparating any appreciable amount of organics, ethyl acetate oracetaldehyde. In one embodiment, the water is removed prior tocondensing the distillate. For example, distillate in vapor phase may befed to an adsorption unit comprising a molecular sieve or a membrane. Insome embodiments, distillate may be condensed to a liquid and fed to amembrane. The heat of vaporization for water is provided to thedistillate to allow water to permeate through the membrane. In preferredembodiments, at least 50% of the water in the distillate is removed,e.g., at least 60% of the water or at least 75% of the water, based onthe total amount of water in the distillate. In more preferredembodiments, from 90 to 99% of the water may be removed from thedistillate. Thus, the resulting ethanol mixture may comprise only aminor amount of water, from 0.01 to 10 wt. %, e.g., from 0.5 to 6 wt. %,or from 0.5 to 4 wt. %. In one embodiment, the ethanol mixture comprisesa water concentration that is less than the amount of water in theethanol/water azeotrope. In order to achieve a water concentration thatis below the amount of water in the ethanol/water azeotrope, a large ofamount of energy is required. Thus, the present invention beneficiallyremoves water from the first distillate to yield an ethanol mixturewithout a large amount of energy. Also, because the ethanol mixturecomprises less water, the need to remove water during the later stage ofproduct separation is also reduced.

In an exemplary embodiment, the energy requirements by the initialcolumn in the process according to the present invention may be lessthan 5.5 MMBtu per ton of refined ethanol, e.g., less than 4.5 MMBtu perton of refined ethanol or less than 3.5 MMBtu per ton of refinedethanol. In some embodiments, the process may operate with higher energyrequirements provided that the total energy requirement is less than theenergy required to remove most of the water from the crude ethanolproduct in the distillate, e.g. more than 65% of the water in the crudeethanol product.

The water that is removed from the distillate may be returned to theinitial column and ultimately removed from the initial column via theresidue. In one embodiment, a portion of the removed water may becondensed and returned below the feed point of the crude ethanol productto the initial column, e.g., near the bottom of the initial column.Depending on the water removal technique, there may be some ethanol andethyl acetate in the removed water and thus it may be desirable torecover these compounds by returning at least a portion of the removedwater to the initial column. Returning the removed water to the initialcolumn may increase the amount of water withdrawn as the residue. Inother embodiments, a portion of the removed water may be fed to aseparation column, e.g. light-ends column, used in recovering an ethanolproduct from the ethanol mixture. The presence of a small amount ofwater, e.g., less than 10 wt. % water based on the total feed, in thelight-ends column may be beneficial in facilitating the separation ofethyl acetate from ethanol. A portion of the removed water may also bepurged as needed to remove water from the system.

The ethanol mixture may be further processed in the light-ends column torecover ethanol. In one embodiment, the C₃+ alcohols are removed priorto the light-ends column and there may be substantially no C₃+ alcoholsin the light-ends column. In some embodiments, it may be desirable tomaintain a concentration of water in the light-ends column. Depending onthe type of water separator, the ethanol mixture may comprises less than0.5 wt. % water. To control the water concentration, a by-pass line maybe used to split the distillate. The split ratio may vary to control theamount of water in feed to the light-ends column. In one embodiment, thesplit ratio may range from 10:1 to 1:10, e.g., from 5:1 to 1:5 or about1:1. Other split ratios may be used when controlling the waterconcentration. The distillate in the by-pass line is not separated toremove water and may be combined or co-fed with the ethanol mixture tothe light-ends column. The combined distillate and ethanol mixture has atotal water concentration of greater than 0.5 wt. %, e.g., greater than2 wt. % or greater than 5 wt. %. In terms of ranges, the total waterconcentration of the combined distillate and ethanol mixture may be from0.5 to 15 wt. %, e.g., from 2 to 12 wt. %, or from 5 to 10 wt. %. Theadditional water for the light-ends column is typically recovered withthe ethanol and separated as desired to provide an ethanol product.

The process of the present invention may use any suitable technique forremoving water from the distillate. For example, water may be removed inthe vapor phase, before condensation, or in the liquid phase. Water maybe removed, for example, using an adsorption unit, membrane, molecularsieves, extractive column distillation, or a combination thereof.Suitable adsorption units include pressure swing adsorption (PSA) unitsand thermal swing adsorption (TSA) units. The adsorption units maycomprises molecular sieves, such as aluminosilicate compounds.

A membrane or an array of membranes may also be employed to separatewater from the distillate. The membrane or array of membranes may beselected from any suitable membrane that is capable of removing apermeate water stream from a stream that also comprises ethanol andethyl acetate.

In a second embodiment, the process of recovering ethanol uses twodistillation columns, in which the residue of the first column comprisesa substantial portion of the ethanol, water, and the acetic acid fromthe crude ethanol product. The residue stream comprising ethanol, water,and acetic acid may be further separated to recover ethanol in a secondcolumn. In addition, the residue also comprises a substantial portion ofthe C₃+ alcohols. One or more sidestreams are withdrawn from the secondcolumn that separates the ethanol from acid acetic and water to regulateC₃+ alcohol concentration.

The residue stream from the first column, for example, may comprise atleast 50% of the ethanol from the crude ethanol product, and morepreferably at least 70%. In terms of ranges, the residue stream maycomprise from 50% to 97.5% of the ethanol from the crude ethanolproduct, and more preferably from 70% to 97.5%. The amount of ethanolfrom the crude ethanol recovered in the residue may be greater than97.5%, e.g. up to 99.9%, when the ethyl acetate concentration in thecrude ethanol product is less than 2 wt. %. In some embodiments,depending on the ethyl acetate concentration, taking too much ethanol inthe residue may cause undesirable leakage of ethyl acetate in theresidue. It is preferred that ethyl acetate is not withdrawn in theresidue and may be present in very low amounts, e.g., less than 100 wppmor less than 50 wppm.

The residue stream comprises a substantial portion of the water and theacetic acid from the crude ethanol product. The residue stream maycomprise at least 80% of the water from the crude ethanol product, andmore preferably at least 90%. In terms of ranges, the residue streampreferably comprises from 80% to 99.4% of the water from the crudeethanol product, and more preferably from 90% to 99.4%. The residuestream may comprise at least 85% of the acetic acid from the crudeethanol product, e.g., at least 90% and more preferably about 100%. Interms of ranges, the residue stream preferably comprises from 85% to100% of the acetic acid from the crude ethanol product, and morepreferably from 90% to 100%. In one embodiment, substantially all of theacetic acid is recovered in the residue stream.

In an exemplary embodiment, the energy requirements by the initialcolumn in the process according to the present invention may be lessthan 5.5 MMBtu per ton of refined ethanol, e.g., less than 4.5 MMBtu perton of refined ethanol or less than 3.5 MMBtu per ton of refinedethanol.

The distillate from the initial column comprises light organics, such asethyl acetate and acetaldehyde. Removing these components from the crudeethanol product in the initial column provides an efficient means forremoving light organics. In addition, the light organics are not carriedover with the ethanol when multiple columns are used, thus reducing theformation of byproducts from the light organics. In one embodiment, thelight organics are returned to the reactor, where the acetaldehyde andthe ethyl acetate are converted to additional ethanol. In someembodiments, the light organics may be separated so that one streamcomprising primarily acetaldehyde or ethyl acetate is returned to thereactor. In another embodiment, the light organics may be purged fromthe system.

Hydrogenation of Acetic Acid

The process of the present invention may be used with any hydrogenationprocess for producing ethanol. The materials, catalysts, reactionconditions, and separation processes that may be used in thehydrogenation of acetic acid are described further below.

The raw materials, acetic acid and hydrogen, used in connection with theprocess of this invention may be derived from any suitable sourceincluding natural gas, petroleum, coal, biomass, and so forth. Asexamples, acetic acid may be produced via methanol carbonylation,acetaldehyde oxidation, ethylene oxidation, oxidative fermentation, andanaerobic fermentation. Methanol carbonylation processes suitable forproduction of acetic acid are described in U.S. Pat. Nos. 7,208,624;7,115,772; 7,005,541; 6,657,078; 6,627,770; 6,143,930; 5,599,976;5,144,068; 5,026,908; 5,001,259; and 4,994,608, the entire disclosuresof which are incorporated herein by reference. Optionally, theproduction of ethanol may be integrated with such methanol carbonylationprocesses.

As petroleum and natural gas prices fluctuate becoming either more orless expensive, methods for producing acetic acid and intermediates suchas methanol and carbon monoxide from alternate carbon sources have drawnincreasing interest. In particular, when petroleum is relativelyexpensive, it may become advantageous to produce acetic acid fromsynthesis gas (“syngas”) that is derived from other available carbonsource. U.S. Pat. No. 6,232,352, the entirety of which is incorporatedherein by reference, for example, teaches a method of retrofitting amethanol plant for the manufacture of acetic acid. By retrofitting amethanol plant, the large capital costs associated with CO generationfor a new acetic acid plant are significantly reduced or largelyeliminated. All or part of the syngas is diverted from the methanolsynthesis loop and supplied to a separator unit to recover CO, which isthen used to produce acetic acid. In a similar manner, hydrogen for thehydrogenation step may be supplied from syngas.

In some embodiments, some or all of the raw materials for theabove-described acetic acid hydrogenation process may be derivedpartially or entirely from syngas. For example, the acetic acid may beformed from methanol and carbon monoxide, both of which may be derivedfrom syngas. The syngas may be formed by partial oxidation reforming orsteam reforming, and the carbon monoxide may be separated from syngas.Similarly, hydrogen that is used in the step of hydrogenating the aceticacid to form the crude ethanol product may be separated from syngas. Thesyngas, in turn, may be derived from variety of carbon sources. Thecarbon source, for example, may be selected from the group consisting ofnatural gas, oil, petroleum, coal, biomass, and combinations thereof.Syngas or hydrogen may also be obtained from bio-derived methane gas,such as bio-derived methane gas produced by landfills or agriculturalwaste.

In another embodiment, the acetic acid used in the hydrogenation stepmay be formed from the fermentation of biomass. The fermentation processpreferably utilizes an acetogenic process or a homoacetogenicmicroorganism to ferment sugars to acetic acid producing little, if any,carbon dioxide as a by-product. The carbon efficiency for thefermentation process preferably is greater than 70%, greater than 80% orgreater than 90% as compared to conventional yeast processing, whichtypically has a carbon efficiency of about 67%. Optionally, themicroorganism employed in the fermentation process is of a genusselected from the group consisting of Clostridium, Lactobacillus,Moorella, Thermoanaerobacter, Propionibacterium, Propionispera,Anaerobiospirillum, and Bacteroides, and in particular, species selectedfrom the group consisting of Clostridium formicoaceticum, Clostridiumbutyricum, Moorella thermoacetica, Thermoanaerobacter kivui,Lactobacillus delbrukii, Propionibacterium acidipropionici,Propionispera arboris, Anaerobiospirillum succinicproducens, Bacteroidesamylophilus and Bacteroides ruminicola. Optionally in this process, allor a portion of the unfermented residue from the biomass, e.g., lignans,may be gasified to form hydrogen that may be used in the hydrogenationstep of the present invention. Exemplary fermentation processes forforming acetic acid are disclosed in U.S. Pat. Nos. 6,509,180;6,927,048; 7,074,603; 7,507,562; 7,351,559; 7,601,865; 7,682,812; and7,888,082, the entireties of which are incorporated herein by reference.See also US Publ. Nos. 2008/0193989 and 2009/0281354, the entireties ofwhich are incorporated herein by reference.

Examples of biomass include, but are not limited to, agriculturalwastes, forest products, grasses, and other cellulosic material, timberharvesting residues, softwood chips, hardwood chips, tree branches, treestumps, leaves, bark, sawdust, off-spec paper pulp, corn, corn stover,wheat straw, rice straw, sugarcane bagasse, switchgrass, miscanthus,animal manure, municipal garbage, municipal sewage, commercial waste,grape pumice, almond shells, pecan shells, coconut shells, coffeegrounds, grass pellets, hay pellets, wood pellets, cardboard, paper,plastic, and cloth. See, e.g., U.S. Pat. No. 7,884,253, the entirety ofwhich is incorporated herein by reference. Another biomass source isblack liquor, a thick, dark liquid that is a byproduct of the Kraftprocess for transforming wood into pulp, which is then dried to makepaper. Black liquor is an aqueous solution of lignin residues,hemicellulose, and inorganic chemicals.

U.S. Pat. No. RE 35,377, also incorporated herein by reference, providesa method for the production of methanol by converting carbonaceousmaterials such as oil, coal, natural gas and biomass materials. Theprocess includes hydrogasification of solid and/or liquid carbonaceousmaterials to obtain a process gas which is steam pyrolized withadditional natural gas to form synthesis gas. The syngas is converted tomethanol which may be carbonylated to acetic acid. The method likewiseproduces hydrogen which may be used in connection with this invention asnoted above. U.S. Pat. No. 5,821,111, which discloses a process forconverting waste biomass through gasification into synthesis gas, andU.S. Pat. No. 6,685,754, which discloses a method for the production ofa hydrogen-containing gas composition, such as a synthesis gas includinghydrogen and carbon monoxide, are incorporated herein by reference intheir entireties.

The acetic acid fed to the hydrogenation reaction may also compriseother carboxylic acids and anhydrides, as well as acetaldehyde andacetone. Preferably, a suitable acetic acid feed stream comprises one ormore of the compounds selected from the group consisting of acetic acid,acetic anhydride, acetaldehyde, ethyl acetate, and mixtures thereof.These other compounds may also be hydrogenated in the processes of thepresent invention. In some embodiments, the presence of carboxylicacids, such as propanoic acid or its anhydride, may be beneficial inproducing propanol. Water may also be present in the acetic acid feed.

Alternatively, acetic acid in vapor form may be taken directly as crudeproduct from the flash vessel of a methanol carbonylation unit of theclass described in U.S. Pat. No. 6,657,078, the entirety of which isincorporated herein by reference. The crude vapor product, for example,may be fed directly to the ethanol synthesis reaction zones of thepresent invention without the need for condensing the acetic acid andlight ends or removing water, saving overall processing costs.

The acetic acid may be vaporized at the reaction temperature, followingwhich the vaporized acetic acid may be fed along with hydrogen in anundiluted state or diluted with a relatively inert carrier gas, such asnitrogen, argon, helium, carbon dioxide and the like. For reactions runin the vapor phase, the temperature should be controlled in the systemsuch that it does not fall below the dew point of acetic acid. In oneembodiment, the acetic acid may be vaporized at the boiling point ofacetic acid at the particular pressure, and then the vaporized aceticacid may be further heated to the reactor inlet temperature. In anotherembodiment, the acetic acid is mixed with other gases before vaporizing,followed by heating the mixed vapors up to the reactor inlettemperature. Preferably, the acetic acid is transferred to the vaporstate by passing hydrogen and/or recycle gas through the acetic acid ata temperature at or below 125° C., followed by heating of the combinedgaseous stream to the reactor inlet temperature.

Some embodiments of the process of hydrogenating acetic acid to formethanol may include a variety of configurations using a fixed bedreactor or a fluidized bed reactor. In many embodiments of the presentinvention, an “adiabatic” reactor can be used; that is, there is littleor no need for internal plumbing through the reaction zone to add orremove heat. In other embodiments, a radial flow reactor or reactors maybe employed, or a series of reactors may be employed with or withoutheat exchange, quenching, or introduction of additional feed material.Alternatively, a shell and tube reactor provided with a heat transfermedium may be used. In many cases, the reaction zone may be housed in asingle vessel or in a series of vessels with heat exchangerstherebetween.

In preferred embodiments, the catalyst is employed in a fixed bedreactor, e.g., in the shape of a pipe or tube, where the reactants,typically in the vapor form, are passed over or through the catalyst.Other reactors, such as fluid or ebullient bed reactors, can beemployed. In some instances, the hydrogenation catalysts may be used inconjunction with an inert material to regulate the pressure drop of thereactant stream through the catalyst bed and the contact time of thereactant compounds with the catalyst particles.

The hydrogenation reaction may be carried out in either the liquid phaseor vapor phase. Preferably, the reaction is carried out in the vaporphase under the following conditions. The reaction temperature may rangefrom 125° C. to 350° C., e.g., from 200° C. to 325° C., from 225° C. to300° C., or from 250° C. to 300° C. The pressure may range from 10 kPato 3000 kPa, e.g., from 50 kPa to 2300 kPa, or from 100 kPa to 1500 kPa.The reactants may be fed to the reactor at a gas hourly space velocity(GHSV) of greater than 500 hr⁻¹, e.g., greater than 1000 hr⁻¹, greaterthan 2500 hr⁻¹ or even greater than 5000 hr⁻¹. In terms of ranges theGHSV may range from 50 hr⁻¹ to 50,000 hr⁻¹, e.g., from 500 hr⁻¹ to30,000 hr⁻¹, from 1000 hr⁻¹ to 10,000 hr⁻¹, or from 1000 hr⁻¹ to 6500hr⁻¹.

The hydrogenation optionally is carried out at a pressure justsufficient to overcome the pressure drop across the catalytic bed at theGHSV selected, although there is no bar to the use of higher pressures,it being understood that considerable pressure drop through the reactorbed may be experienced at high space velocities, e.g., 5000 hr⁻¹ or6,500 hr⁻¹.

Although the reaction consumes two moles of hydrogen per mole of aceticacid to produce one mole of ethanol, the actual molar ratio of hydrogento acetic acid in the feed stream may vary from about 100:1 to 1:100,e.g., from 50:1 to 1:50, from 20:1 to 1:2, or from 12:1 to 1:1. Mostpreferably, the molar ratio of hydrogen to acetic acid is greater than2:1, e.g., greater than 4:1 or greater than 8:1.

Contact or residence time can also vary widely, depending upon suchvariables as amount of acetic acid, catalyst, reactor, temperature, andpressure. Typical contact times range from a fraction of a second tomore than several hours when a catalyst system other than a fixed bed isused, with preferred contact times, at least for vapor phase reactions,of from 0.1 to 100 seconds, e.g., from 0.3 to 80 seconds or from 0.4 to30 seconds.

The hydrogenation of acetic acid to form ethanol is preferably conductedin the presence of a hydrogenation catalyst. Suitable hydrogenationcatalysts include catalysts comprising a first metal and optionally oneor more of a second metal, a third metal or any number of additionalmetals, optionally on a catalyst support. The first and optional secondand third metals may be selected from Group IB, IIB, IIIB, IVB, VB, VIB,VIIB, VIII transition metals, a lanthanide metal, an actinide metal or ametal selected from any of Groups IIIA, IVA, VA, and VIA. Preferredmetal combinations for some exemplary catalyst compositions includeplatinum/tin, platinum/ruthenium, platinum/rhenium, palladium/ruthenium,palladium/rhenium, cobalt/palladium, cobalt/platinum, cobalt/chromium,cobalt/ruthenium, cobalt/tin, silver/palladium, copper/palladium,copper/zinc, nickel/palladium, gold/palladium, ruthenium/rhenium, andruthenium/iron. Exemplary catalysts are further described in U.S. Pat.No. 7,608,744 and U.S. Pub. No. 2010/0029995, the entireties of whichare incorporated herein by reference. In another embodiment, thecatalyst comprises a Co/Mo/S catalyst of the type described in U.S. Pub.No. 2009/0069609, the entirety of which is incorporated herein byreference.

In one embodiment, the catalyst comprises a first metal selected fromthe group consisting of copper, iron, cobalt, nickel, ruthenium,rhodium, palladium, osmium, iridium, platinum, titanium, zinc, chromium,rhenium, molybdenum, and tungsten. Preferably, the first metal isselected from the group consisting of platinum, palladium, cobalt,nickel, and ruthenium. More preferably, the first metal is selected fromplatinum and palladium. In embodiments of the invention where the firstmetal comprises platinum, it is preferred that the catalyst comprisesplatinum in an amount less than 5 wt. %, e.g., less than 3 wt. % or lessthan 1 wt. %, due to the high commercial demand for platinum.

As indicated above, in some embodiments, the catalyst further comprisesa second metal, which typically would function as a promoter. Ifpresent, the second metal preferably is selected from the groupconsisting of copper, molybdenum, tin, chromium, iron, cobalt, vanadium,tungsten, palladium, platinum, lanthanum, cerium, manganese, ruthenium,rhenium, gold, and nickel. More preferably, the second metal is selectedfrom the group consisting of copper, tin, cobalt, rhenium, and nickel.More preferably, the second metal is selected from tin and rhenium.

In certain embodiments where the catalyst includes two or more metals,e.g., a first metal and a second metal, the first metal is present inthe catalyst in an amount from 0.1 to 10 wt. %, e.g., from 0.1 to 5 wt.%, or from 0.1 to 3 wt. %. The second metal preferably is present in anamount from 0.1 to 20 wt. %, e.g., from 0.1 to 10 wt. %, or from 0.1 to5 wt. %. For catalysts comprising two or more metals, the two or moremetals may be alloyed with one another or may comprise a non-alloyedmetal solution or mixture.

The preferred metal ratios may vary depending on the metals used in thecatalyst. In some exemplary embodiments, the mole ratio of the firstmetal to the second metal is from 10:1 to 1:10, e.g., from 4:1 to 1:4,from 2:1 to 1:2, from 1.5:1 to 1:1.5 or from 1.1:1 to 1:1.1.

The catalyst may also comprise a third metal selected from any of themetals listed above in connection with the first or second metal, solong as the third metal is different from the first and second metals.In preferred aspects, the third metal is selected from the groupconsisting of cobalt, palladium, ruthenium, copper, zinc, platinum, tin,and rhenium. More preferably, the third metal is selected from cobalt,palladium, and ruthenium. When present, the total weight of the thirdmetal preferably is from 0.05 to 4 wt. %, e.g., from 0.1 to 3 wt. %, orfrom 0.1 to 2 wt. %.

In addition to one or more metals, in some embodiments of the presentinvention the catalysts further comprise a support or a modifiedsupport. As used herein, the term “modified support” refers to a supportthat includes a support material and a support modifier, which adjuststhe acidity of the support material.

The total weight of the support or modified support, based on the totalweight of the catalyst, preferably is from 75 to 99.9 wt. %, e.g., from78 to 97 wt. %, or from 80 to 95 wt. %. In preferred embodiments thatutilize a modified support, the support modifier is present in an amountfrom 0.1 to 50 wt. %, e.g., from 0.2 to 25 wt. %, from 0.5 to 15 wt. %,or from 1 to 8 wt. %, based on the total weight of the catalyst. Themetals of the catalysts may be dispersed throughout the support, layeredthroughout the support, coated on the outer surface of the support(i.e., egg shell), or decorated on the surface of the support.

As will be appreciated by those of ordinary skill in the art, supportmaterials are selected such that the catalyst system is suitably active,selective and robust under the process conditions employed for theformation of ethanol.

Suitable support materials may include, for example, stable metaloxide-based supports or ceramic-based supports. Preferred supportsinclude silicaceous supports, such as silica, silica/alumina, a GroupIIA silicate such as calcium metasilicate, pyrogenic silica, high puritysilica, and mixtures thereof. Other supports may include, but are notlimited to, iron oxide, alumina, titania, zirconia, magnesium oxide,carbon, graphite, high surface area graphitized carbon, activatedcarbons, and mixtures thereof.

As indicated, the catalyst support may be modified with a supportmodifier. In some embodiments, the support modifier may be an acidicmodifier that increases the acidity of the catalyst. Suitable acidicsupport modifiers may be selected from the group consisting of: oxidesof Group IVB metals, oxides of Group VB metals, oxides of Group VIBmetals, oxides of Group VIIB metals, oxides of Group VIIIB metals,aluminum oxides, and mixtures thereof. Acidic support modifiers includethose selected from the group consisting of TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅,Al₂O₃, B₂O₃, P₂O₅, and Sb₂O₃. Preferred acidic support modifiers includethose selected from the group consisting of TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅,and Al₂O₃. The acidic modifier may also include WO₃, MoO₃, Fe₂O₃, Cr₂O₃,V₂O₅, MnO₂, CuO, Co₂O₃, and Bi₂O₃.

In another embodiment, the support modifier may be a basic modifier thathas a low volatility or no volatility. Such basic modifiers, forexample, may be selected from the group consisting of: (i) alkalineearth metal oxides, (ii) alkali metal oxides, (iii) alkaline earth metalmetasilicates, (iv) alkali metal metasilicates, (v) Group IIB metaloxides, (vi) Group IIB metal metasilicates, (vii) Group IIIB metaloxides, (viii) Group IIIB metal metasilicates, and mixtures thereof. Inaddition to oxides and metasilicates, other types of modifiers includingnitrates, nitrites, acetates, and lactates may be used. Preferably, thesupport modifier is selected from the group consisting of oxides andmetasilicates of any of sodium, potassium, magnesium, calcium, scandium,yttrium, and zinc, as well as mixtures of any of the foregoing. Morepreferably, the basic support modifier is a calcium silicate, and evenmore preferably calcium metasilicate (CaSiO₃). If the basic supportmodifier comprises calcium metasilicate, it is preferred that at least aportion of the calcium metasilicate is in crystalline form.

A preferred silica support material is SS61138 High Surface Area (HSA)Silica Catalyst Carrier from Saint Gobain NorPro. The Saint-GobainNorPro SS61138 silica exhibits the following properties: containsapproximately 95 wt. % high surface area silica; surface area of about250 m²/g; median pore diameter of about 12 nm; average pore volume ofabout 1.0 cm³/g as measured by mercury intrusion porosimetry and apacking density of about 0.352 g/cm³ (22 lb/ft³).

A preferred silica/alumina support material is KA-160 silica spheresfrom Sud Chemie having a nominal diameter of about 5 mm, a density ofabout 0.562 g/ml, an absorptivity of about 0.583 g H₂O/g support, asurface area of about 160 to 175 m²/g, and a pore volume of about 0.68ml/g.

The catalyst compositions suitable for use with the present inventionpreferably are formed through metal impregnation of the modifiedsupport, although other processes such as chemical vapor deposition mayalso be employed. Such impregnation techniques are described in U.S.Pat. Nos. 7,608,744 and 7,863,489 and U.S. Pub. No. 2010/0197485referred to above, the entireties of which are incorporated herein byreference.

In particular, the hydrogenation of acetic acid may achieve favorableconversion of acetic acid and favorable selectivity and productivity toethanol. For purposes of the present invention, the term “conversion”refers to the amount of acetic acid in the feed that is converted to acompound other than acetic acid. Conversion is expressed as a molepercentage based on acetic acid in the feed. The conversion may be atleast 10%, e.g., at least 20%, at least 40%, at least 50%, at least 60%,at least 70% or at least 80%. Although catalysts that have highconversions are desirable, such as at least 80% or at least 90%, in someembodiments a low conversion may be acceptable at high selectivity forethanol. It is, of course, well understood that in many cases, it ispossible to compensate for conversion by appropriate recycle streams oruse of larger reactors, but it is more difficult to compensate for poorselectivity.

Selectivity is expressed as a mole percent based on converted aceticacid. It should be understood that each compound converted from aceticacid has an independent selectivity and that selectivity is independentfrom conversion. For example, if 60 mole % of the converted acetic acidis converted to ethanol, we refer to the ethanol selectivity as 60%.Preferably, the catalyst selectivity to ethoxylates is at least 60%,e.g., at least 70%, or at least 80%. As used herein, the term“ethoxylates” refers specifically to the compounds ethanol,acetaldehyde, and ethyl acetate. Preferably, the selectivity to ethanolis at least 80%, e.g., at least 85% or at least 88%. Preferredembodiments of the hydrogenation process also have low selectivity toundesirable products, such as methane, ethane, and carbon dioxide. Theselectivity to these undesirable products preferably is less than 4%,e.g., less than 2% or less than 1%. More preferably, these undesirableproducts are present in undetectable amounts. Formation of alkanes maybe low, and ideally less than 2%, less than 1%, or less than 0.5% of theacetic acid passed over the catalyst is converted to alkanes, which havelittle value other than as fuel.

The term “productivity,” as used herein, refers to the grams of aspecified product, e.g., ethanol, formed during the hydrogenation basedon the kilograms of catalyst used per hour. A productivity of at least100 grams of ethanol per kilogram of catalyst per hour, e.g., at least400 grams of ethanol per kilogram of catalyst per hour or at least 600grams of ethanol per kilogram of catalyst per hour, is preferred. Interms of ranges, the productivity preferably is from 100 to 3,000 gramsof ethanol per kilogram of catalyst per hour, e.g., from 400 to 2,500grams of ethanol per kilogram of catalyst per hour or from 600 to 2,000grams of ethanol per kilogram of catalyst per hour.

Operating under the conditions of the present invention may result inethanol production on the order of at least 0.1 tons of ethanol perhour, e.g., at least 1 ton of ethanol per hour, at least 5 tons ofethanol per hour, or at least 10 tons of ethanol per hour. Larger scaleindustrial production of ethanol, depending on the scale, generallyshould be at least 1 ton of ethanol per hour, e.g., at least 15 tons ofethanol per hour or at least 30 tons of ethanol per hour. In terms ofranges, for large scale industrial production of ethanol, the process ofthe present invention may produce from 0.1 to 160 tons of ethanol perhour, e.g., from 15 to 160 tons of ethanol per hour or from 30 to 80tons of ethanol per hour. Ethanol production from fermentation, due theeconomies of scale, typically does not permit the single facilityethanol production that may be achievable by employing embodiments ofthe present invention.

In various embodiments of the present invention, the crude ethanolproduct produced by the hydrogenation process, before any subsequentprocessing, such as purification and separation, will typically compriseacetic acid, ethanol and water. Exemplary compositional ranges for thecrude ethanol product are provided in Table 1. The “others” identifiedin Table 1 may include, for example, esters, ethers, aldehydes, ketones,alkanes, and carbon dioxide.

TABLE 1 CRUDE ETHANOL PRODUCT COMPOSITIONS Conc. Conc. Conc. Conc.Component (wt. %) (wt. %) (wt. %) (wt. %) Ethanol 5 to 70 15 to 70 15 to50 25 to 50 Acetic Acid 0 to 90 0 to 70 15 to 60 20 to 50 Water 5 to 405 to 30 10 to 30 10 to 26 Ethyl Acetate 0 to 30 0 to 20 1 to 12 3 to 10Acetaldehyde 0 to 10 0 to 3 0.1 to 3 0.2 to 2 C₃+ Alcohols 0.0001 to 80.0001 to 1 0.0001 to 0.01 — Others 0.1 to 10 0.1 to 6 0.1 to 4 —

In one embodiment, the crude ethanol product comprises acetic acid in anamount less than 20 wt. %, e.g., less than 15 wt. %, less than 10 wt. %or less than 5 wt. %. In terms of ranges, the acetic acid concentrationof Table 1 may range from 0.1 wt. % to 20 wt. %, e.g., 0.2 wt. % to 15wt. %, from 0.5 wt. % to 10 wt. % or from 1 wt. % to 5 wt. %. Inembodiments having lower amounts of acetic acid, the conversion ofacetic acid is preferably greater than 75%, e.g., greater than 85% orgreater than 90%. In addition, the selectivity to ethanol may also bepreferably high, and is preferably greater than 75%, e.g., greater than85% or greater than 90%.

Ethanol Recovery

The crude ethanol product containing C₃+ alcohols may be treated tocontrol the amount of C₃+ alcohols in the ethanol product, as shown byexemplary hydrogenation systems 100 in FIGS. 1 and 2. Each hydrogenationsystem 100 provides a suitable hydrogenation reactor and a process forseparating ethanol from the crude reaction mixture according to anembodiment of the invention. System 100 comprises reaction zone 101 andseparation zone 102. Further modifications and additional components toreaction zone 101 and separation zone 102 are described below.

Reaction zone 101 comprises reactor 103, hydrogen feed line 104 andacetic acid feed line 105. Hydrogen and acetic acid are fed to avaporizer 106 via lines 104 and 105, respectively, to create a vaporfeed stream in line 107 that is directed to reactor 103. In oneembodiment, lines 104 and 105 may be combined and jointly fed to thevaporizer 106. The temperature of the vapor feed stream in line 107 ispreferably from 100° C. to 350° C., e.g., from 120° C. to 310° C. orfrom 150° C. to 300° C. Any feed that is not vaporized is removed fromvaporizer 106, and may be recycled or discarded. In addition, althoughline 107 is shown as being directed to the top of reactor 103, line 107may be directed to the side, upper portion, or bottom of reactor 103.

Reactor 103 contains the catalyst that is used in the hydrogenation ofthe carboxylic acid, preferably acetic acid. In one embodiment, one ormore guard beds (not shown) may be used upstream of the reactor,optionally upstream of vaporizer 106, to protect the catalyst frompoisons or undesirable impurities contained in the feed orreturn/recycle streams. Such guard beds may be employed in the vapor orliquid streams. Suitable guard bed materials may include, for example,carbon, silica, alumina, ceramic, or resins. In one aspect, the guardbed media is functionalized, e.g., silver functionalized, to trapparticular species such as sulfur or halogens. During the hydrogenationprocess, a crude ethanol product stream is withdrawn, preferablycontinuously, from reactor 103 via line 110.

The crude ethanol product stream may be condensed and fed to a separator111, which, in turn, forms a vapor stream 112 and a liquid stream 113.In some embodiments, separator 111 may comprise a flasher or a knockoutpot. The separator 111 may operate at a temperature of from 20° C. to250° C., e.g., from 30° C. to 225° C. or from 60° C. to 200° C. Thepressure of separator 111 may be from 50 kPa to 2000 kPa, e.g., from 75kPa to 1500 kPa or from 100 kPa to 1000 kPa. Optionally, the crudeethanol product in line 110 may pass through one or more membranes toseparate hydrogen and/or other non-condensable gases.

The vapor stream 112 exiting separator 111 may comprise hydrogen andhydrocarbons, and may be purged and/or returned to reaction zone 101. Asshown, vapor stream 112 is combined with the hydrogen feed 104 andco-fed to vaporizer 106. In some embodiments, the returned vapor stream112 may be compressed before being combined with hydrogen feed 104.

In FIG. 1, the liquid stream 113 from separator 111 is withdrawn anddirected as a feed composition to the side of first distillation column115, also referred to as an “acid-water column.” In one embodiment, thecontents of liquid stream 113 are substantially similar to the crudeethanol product obtained from the reactor, except that the compositionhas been depleted of hydrogen, carbon dioxide, methane or ethane, whichhave been removed by separator 106. Accordingly, liquid stream 113 mayalso be referred to as a crude ethanol product. Exemplary components ofliquid stream 113 are provided in Table 2. It should be understood thatliquid stream 113 may contain other components, not listed in Table 2.

TABLE 2 COLUMN FEED COMPOSITION (Liquid Stream 113) Conc. (wt. %) Conc.(wt. %) Conc. (wt. %) Ethanol 5 to 70 10 to 60 15 to 50 Acetic Acid  <905 to 80 15 to 70 Water 5 to 45 5 to 30 10 to 30 Ethyl Acetate  <35 0.001to 15 1 to 12 Acetaldehyde  <10 0.001 to 3 0.1 to 3 Acetal <5 0.001 to 20.005 to 1 Acetone <5 0.0005 to 0.05 0.001 to 0.03 C₃+ Alcohols <8<1     <0.1  Other Esters <5 <0.005 <0.001 Other Ethers <5 <0.005 <0.001

The amounts indicated as less than (<) in the tables throughout thepresent specification are preferably not present and if present may bepresent in trace amounts or in amounts greater than 0.0001 wt. %.

The “other esters” in Table 2 may include, but are not limited to, ethylpropionate, methyl acetate, isopropyl acetate, n-propyl acetate, n-butylacetate or mixtures thereof. The “other ethers” in Table 2 may include,but are not limited to, diethyl ether, methyl ethyl ether, isobutylethyl ether or mixtures thereof. In should be understood that theseother components may be carried through in any of the distillate orresidue streams described herein and will not be further describedherein, unless indicated otherwise.

Optionally, crude ethanol product in line 110 or in liquid stream 113may be further fed to an esterification reactor, hydrogenolysis reactor,or combination thereof. An esterification reactor may be used to consumeacetic acid present in the crude ethanol product to further reduce theamount of acetic acid to be removed. Hydrogenolysis may be used toconvert ethyl acetate in the crude ethanol product to ethanol.

In FIG. 1, liquid stream 113 is fed to the first column 115 to yield afirst distillate 116 and first residue 117. A sidestream 118 comprisingC₃+ alcohols is also withdrawn from first column 115. Liquid stream 113may be introduced in the middle or lower portion of first column 115.Sidestream 118 may be withdrawn above the fed point of liquid stream113, preferably in the upper portion of first column 115, and below thereflux of the distillate. First column 115 may be tray column havingfrom 1 to 150 trays, e.g., from 10 to 100 trays, from 20 to 95 trays orfrom 30 to 75 trays. For purposes of this invention, it is understoodthat tray 1 is the top tray. In one exemplary embodiment, first column115 comprises 72 trays and sidestream 118 is withdrawn above the 30thtray, and more preferably between the 2nd and 25th tray. The location ofthe sidestream 118 may vary depending on the size of first column 115.In addition, although one sidestream 118 is shown in FIG. 1, it isunderstood that there may be multiple sidestreams.

In preferred embodiments, the C₃+ alcohols concentration in firstdistillate 116 is optimized using sidestream 118 to be within operatinglimits for ethanol standards, i.e. industrial ethanol standards or fuelethanol standards, but in some embodiments it may be desirable to removesubstantially all of the C₃+ alcohols from the first distillate in line116. The concentration of C₃+ alcohols in a sidestream 118 may vary asnecessary to control the C₃+ alcohols concentration in distillate and/orresidue of column 115. For example, in some embodiments, a sidestream118 may comprise up to 99 wt. % ethanol, ethyl acetate, and/or water,e.g., up to 95 wt. % or up to 90 wt. %, and less than 10 wt. % C₃+alcohols, e.g., less than 5 wt. % or less than 1 wt. %.

In one embodiment, no entrainers are added to first column 115. Waterand acetic acid, along with any other heavy components, if present, areremoved from liquid stream 113 and are withdrawn, preferablycontinuously, as a first residue in line 117. Preferably, a substantialportion of the water in the crude ethanol mixture that is fed to firstcolumn 115 may be removed in the first residue, for example, up to about75% or to about 90% of the water from the crude ethanol mixture. In oneembodiment, 30 to 90% of the water in the crude ethanol mixture isremoved in the residue, e.g., from 40 to 88% of the water or from 50 to84% of the water.

When first column 115 is operated under about 170 kPa, the temperatureof the residue exiting in line 117 preferably is from 90° C. to 130° C.,e.g., from 95° C. to 120° C. or from 100° C. to 115° C. The temperatureof the distillate exiting in line 116 preferably is from 60° C. to 90°C., e.g., from 65° C. to 85° C. or from 70° C. to 80° C. In someembodiments, the pressure of first column 115 may also range from 0.1kPa to 510 kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa.

The first distillate in line 116 comprises some water in addition toethanol and other organics. In terms of ranges, the water concentrationin the first distillate in line 116 preferably is from 4 wt. % to 38 wt.%, e.g., from 7 wt. % to 32 wt. %, or from 7 to 25 wt. %. A portion offirst distillate in line 119 may be condensed and refluxed, for example,at a ratio of from 10:1 to 1:10, e.g., from 3:1 to 1:3 or from 1:2 to2:1. It is understood that reflux ratios may vary with the number ofstages, feed locations, column efficiency and/or feed composition.Operating with a reflux ratio of greater than 3:1 may be less preferredbecause more energy may be required to operate the first column 115. Thecondensed portion of the first distillate may also be fed to a secondcolumn 120.

In some embodiments the first distillate may be split into equalportions, while in other embodiments, all of the first distillate may becondensed via line 119 or all of the first distillate may be processedin the water separation unit 122.

As shown, the remaining portion of the first distillate in line 121 isfed to a water separation unit 122. Water separation unit 122 may be anadsorption unit, membrane, molecular sieves, extractive columndistillation, or a combination thereof. A membrane or an array ofmembranes may also be employed to separate water from the distillate.The membrane or array of membranes may be selected from any suitablemembrane that is capable of removing a permeate water stream from astream that also comprises ethanol and ethyl acetate.

In a preferred embodiment, water separator 122 is a pressure swingadsorption (PSA) unit. The PSA unit is optionally operated at atemperature from 30° C. to 160° C., e.g., from 80° C. to 140° C., and apressure of from 0.01 kPa to 550 kPa, e.g., from 1 kPa to 150 kPa. ThePSA unit may comprise from two to five beds. Water separator 122 mayremove at least 95% of the water from the portion of first distillate inline 121, and more preferably from 99% to 99.99% of the water from thefirst distillate, in a water stream 123. All or a portion of waterstream 123 may be returned to first column 115, where the waterpreferably is ultimately recovered in the first residue in line 117.Additionally or alternatively, all or a portion of water stream 123 maybe removed from the hydrogenation system via line 124. The remainingportion of first distillate exits the water separator 122 as ethanolmixture stream 125. Ethanol mixture stream 125 may have a low waterconcentration of less than 10 wt. %, e.g., less than 6 wt. % or lessthan 2 wt. %.

Exemplary components of ethanol mixture stream 125 and first residue inline 117 are provided in Table 3 below. Preferably, there are nodetectable amounts of C₃+ alcohols in the first residue. In addition,the concentration of C₃+ alcohols in the distillate is reduced and thusthe concentration of C₃+ alcohols in ethanol mixture stream 125 is alsoreduced. It should also be understood that these streams may alsocontain other components, not listed, such as components derived fromthe feed.

TABLE 3 FIRST COLUMN WITH PSA (FIG. 1) Conc. (wt. %) Conc. (wt. %) Conc.(wt. %) Ethanol Mixture Stream Ethanol 20 to 95 30 to 95 40 to 95 Water <10 0.01 to 6 0.1 to 2 Acetic Acid <2 0.001 to 0.5 0.01 to 0.2 EthylAcetate  <60 1 to 55 5 to 55 Acetaldehyde  <10 0.001 to 5 0.01 to 4Acetal   <0.1 <0.1  <0.05 Acetone   <0.05 0.001 to 0.03 0.01 to 0.025C₃+ alcohols <1 0.0001 to 0.5 0.005 to 0.4 Residue Acetic Acid  <90 1 to50 2 to 35 Water 30 to 100 45 to 95 60 to 90 Ethanol <1 <0.9 <0.3

In an optional embodiment, all or a portion of either or both the firstresidue in line 117 and/or the separated stream in line 124 may bedirected to the carbonylation system to serve as an extraction medium.

Preferably, ethanol mixture stream 125 is not returned or refluxed tofirst column 115 but rather the condensed portion of the firstdistillate in line 119 is refluxed. The condensed portion of the firstdistillate in line 119 may be combined with ethanol mixture stream 125to control the water concentration fed to the second column 120. In FIG.1, the condensed portion in line 123 and ethanol mixture stream 125 areco-fed to second column 120. In other embodiments, the condensed portionin line 123 and ethanol mixture stream 125 may be separately fed tosecond column 120. The combined distillate and ethanol mixture has atotal water concentration of greater than 0.5 wt. %, e.g., greater than2 wt. % or greater than 5 wt. %. In terms of ranges, the total waterconcentration of the combined distillate and ethanol mixture may be from0.5 to 15 wt. %, e.g., from 2 to 12 wt. %, or from 5 to 10 wt. %.

The second column 120 in FIG. 1, also referred to as the “light endscolumn,” removes ethyl acetate and acetaldehyde from the firstdistillate in line 119 and/or ethanol mixture stream 125. Ethyl acetateand acetaldehyde are removed as a second distillate in line 126 andethanol is removed as the second residue in line 127. Because C3+alcohol concentrations have been reduced in first column 115 it may notbe necessary to remove any sidestreams from second column 120. In anoptional embodiment, ethanol may be removed from second column 120 in asidestream and C3+ alcohols may be removed as the residue.

Second column 120 may be a tray column or packed column. In oneembodiment, second column 120 is a tray column having from 5 to 120trays, e.g., from 15 to 100 trays or from 20 to 90 trays. In oneembodiment, second column 120 may operate at a pressure ranging from 0.1kPa to 510 kPa, e.g., from 10 kPa to 450 kPa or from 50 kPa to 350 kPa.In one embodiment, it may be preferred to operate second column 120 at apressure less than atmospheric pressure to decrease the energy requiredto separate ethyl acetate and ethanol. Although the temperature ofsecond column 120 may vary, when at about 20 kPa to 70 kPa, thetemperature of the second residue exiting in line 127 preferably is from30° C. to 75° C., e.g., from 35° C. to 70° C. or from 40° C. to 65° C.The temperature of the second distillate exiting in line 126 preferablyis from 20° C. to 55° C., e.g., from 25° C. to 50° C. or from 30° C. to45° C.

The total concentration of water fed to second column 120 preferably isless than 10 wt. %, as discussed above. When first distillate in line119 and/or ethanol mixture stream 125 comprises minor amounts of water,e.g., less than 1 wt. % or less than 0.5 wt. %, additional water may befed to the second column 120 as an extractive agent in the upper portionof the column. A sufficient amount of water is preferably added via theextractive agent such that the total concentration of water fed tosecond column 120 is from 1 to 10 wt. % water, e.g., from 2 to 6 wt. %,based on the total weight of all components fed to second column 120. Ifthe extractive agent comprises water, the water may be obtained from anexternal source or from an internal return/recycle line from one or moreof the other columns or water separators.

Suitable extractive agents may also include, for example,dimethylsulfoxide; glycerine; diethylene glycol; 1-naphthol;hydroquinone; N,N′-dimethylformamide; 1,4-butanediol; ethyleneglycol-1,5-pentanediol; propylene glycol-tetraethyleneglycol-polyethylene glycol; glycerine-propylene glycol-tetraethyleneglycol-1,4-butanediol; ethyl ether; methyl formate; cyclohexane;N,N′-dimethyl-1,3-propanediamine; N,N′-dimethylethylenediamine;diethylene triamine; hexamethylene diamine; 1,3-diaminopentane; analkylated thiophene; dodecane; tridecane; tetradecane; chlorinatedparaffins; or a combination thereof. When extractive agents are used, asuitable recovery system, such as a further distillation column, may beused to recycle the extractive agent.

The second distillate in line 126, which comprises ethyl acetate and/oracetaldehyde, preferably is refluxed as shown in FIG. 1, for example, ata reflux ratio of from 1:30 to 30:1, e.g., from 1:10 to 10:1 or from 1:3to 3:1. In one aspect, not shown, the second distillate 126 or a portionthereof may be returned to reactor 103.

In one embodiment, the second distillate in line 126 and/or a refinedsecond distillate, or a portion of either or both streams, may befurther separated to produce an acetaldehyde-containing stream and anethyl acetate-containing stream. For example, an additional column (notshown) may be used to separate second distillate in line 126. This mayallow a portion of either the resulting acetaldehyde-containing streamor ethyl acetate-containing stream to be recycled to reactor 103 whilepurging the other stream. The purge stream may be valuable as a sourceof either ethyl acetate and/or acetaldehyde.

Exemplary components for the second distillate and second residuecompositions for the second column 120 are provided in Table 4, below.It should be understood that the distillate and residue may also containother components, not listed in Table 4.

TABLE 4 SECOND COLUMN (FIG. 1) Conc. (wt. %) Conc. (wt. %) Conc. (wt. %)Second Distillate Ethyl Acetate 5 to 90 10 to 80 15 to 75 Acetaldehyde<60 1 to 40 1 to 35 Ethanol <45 0.001 to 40 0.01 to 35 Water <20 0.01 to10 0.1 to 5 Second Residue Ethanol 80 to 99.5 85 to 97 60 to 95 Water<20 0.001 to 15 0.01 to 10 Ethyl Acetate <1  0.001 to 2 0.001 to 0.5Acetic Acid  <0.5 <0.01 0.001 to 0.01 C₃+ alcohols <1  0.0001 to 0.50.005 to 0.4

Another exemplary two column separation scheme is shown in FIG. 2.Similar to FIG. 1, liquid stream 113 is obtained from reaction zone 101and is introduced in the upper part of first column 130, e.g., upperhalf or upper third. For purposes of convenience, the columns in eachexemplary separation process, may be referred as the first, second,etc., columns, but it is understood that first column 115 in FIG. 1operates differently than the first column 130 of FIG. 2. In oneembodiment, no entrainers are added to first column 130. In first column130, a weight majority of the ethanol, water, acetic acid, and otherheavy components, if present, are removed from liquid stream 113 and arewithdrawn, preferably continuously, as the first residue in line 131.First column 130 also forms an overhead distillate, which is withdrawnin line 132, and which may be condensed and refluxed, for example, at aratio of from 30:1 to 1:30, e.g., from 10:1 to 1:10 or from 1:5 to 5:1.The first distillate in line 132 preferably comprises a weight majorityof the ethyl acetate from liquid line 113. In addition, distillate inline 132 may also comprise acetaldehyde.

As shown in FIG. 2, there are no sidestreams taken from first column 130to reduce the concentration of heavy alcohols. In an optionalembodiment, a sidestream comprising the weight majority of the ethanol,water, acetic acid may be withdrawn from a sidestream near the base offirst column and C3+ alcohols removed as the residue.

When column 130 is operated under about 170 kPa, the temperature of theresidue exiting in line 131 preferably is from 70° C. to 155° C., e.g.,from 90° C. to 130° C. or from 100° C. to 110° C. The base of column 130may be maintained at a relatively low temperature by withdrawing aresidue stream comprising ethanol, water, and acetic acid, therebyproviding an energy efficiency advantage. The temperature, at 170 kPa,of the distillate exiting in line 132 preferably is from 75° C. to 100°C., e.g., from 75° C. to 83° C. or from 81° C. to 84° C.

In one embodiment, column 130 of FIG. 2 may be operated at a temperaturewhere most of the water, ethanol, and acetic acid are removed from theresidue stream and only a small amount of ethanol and water is collectedin the distillate stream due to the formation of binary and tertiaryazeotropes. The weight ratio of water in the residue in line 131 towater in the distillate in line 132 may be greater than 1:1, e.g.,greater than 2:1. The weight ratio of ethanol in the residue to ethanolin the distillate may be greater than 1:1, e.g., greater than 2:1.

The amount of acetic acid in the first residue may vary dependingprimarily on the conversion in reactor 103. In one embodiment, when theconversion is high, e.g., greater than 90%, the amount of acetic acid inthe first residue may be less than 10 wt. %, e.g., less than 5 wt. % orless than 2 wt. %. In other embodiments, when the conversion is lower,e.g., less than 90%, the amount of acetic acid in the first residue maybe greater than 10 wt. %.

The distillate preferably is substantially free of acetic acid, e.g.,comprising less than 1000 wppm, less than 500 wppm or less than 100 wppmacetic acid. The distillate may be purged from the system or recycled inwhole or part to reactor 103. In some embodiments, the distillate may befurther separated into an acetaldehyde stream and an ethyl acetatestream. Either of these streams may be returned to the reactor 103 orseparated from system as a separate product.

To recover ethanol, the residue in line 131 may be further separated ina second column 133, also referred to as an “acid separation column.” Anacid separation column may be used when the acetic acid concentration inthe first residue is greater than 1 wt. %, e.g., greater than 5 wt. %.The first residue in line 131 is introduced to second column 133preferably in the top part of column 133, e.g., top half or top third.Second column 133 yields a second residue in line 134 comprising aceticacid and water, and a second distillate in line 135 comprising ethanol.

A sidestream 136 comprising C₃+ alcohols is also withdrawn from secondcolumn 133. Sidestream 136 may be withdrawn above the feed point offirst residue in line 131, preferably in the upper portion of secondcolumn 133, and below the reflux of the distillate. Second column 133may be a tray column or packed column. Second column 133 may be a traycolumn having from 1 to 150 trays, e.g., from 10 to 100 trays, from 20to 95 trays or from 30 to 75 trays. For purposes of this invention, itis understood that the tray 1 is the top tray. In one exemplaryembodiment, second column 133 comprises 72 trays and sidestream 136 iswithdrawn above the 20th tray, and more preferably between the 3nd and15th tray. The location of the sidestream 136 may vary depending on thesize of second column 133. In addition, although one sidestream 136 isshown in FIG. 2, it is understood that there may be multiplesidestreams.

In preferred embodiments, the C₃+ alcohols concentration in seconddistillate 135 is optimized using sidestream 136 to be within operatinglimits for ethanol standards, i.e. industrial ethanol standards or fuelethanol standards, but in some embodiments it may be desirable to removesubstantially all of the C₃+ alcohols from the second distillate in line135. The concentration of C₃+ alcohols in a sidestream 136 may vary asnecessary to control the C₃+ alcohols concentration in distillate and/orresidue of column 133. For example, in some embodiments, a sidestream136 may comprise up to 99 wt. % ethanol, ethyl acetate, and/or water,e.g., up to 95 wt. % or up to 90 wt. %, and less than 10 wt. % C₃+alcohols, e.g., less than 5 wt. % or less than 1 wt. %.

Although the temperature and pressure of second column 133 may vary,when at atmospheric pressure the temperature of the second residueexiting in line 134 preferably is from 95° C. to 130° C., e.g., from100° C. to 125° C. or from 110° C. to 120° C. The temperature of thesecond distillate exiting in line 136 preferably is from 60° C. to 105°C., e.g., from 75° C. to 100° C. or from 80° C. to 100° C. The pressureof second column 133 may range from 0.1 kPa to 510 kPa, e.g., from 1 kPato 475 kPa or from 1 kPa to 375 kPa. Exemplary components for thedistillate and residue compositions for second column 133 are providedin Table 5 below. It should be understood that the distillate andresidue may also contain other components, not listed in Table 5.

TABLE 5 SECOND COLUMN (FIG. 2) Conc. (wt. %) Conc. (wt. %) Conc. (wt. %)Second Distillate Ethanol 70 to 99.9 75 to 98 80 to 95 Ethyl Acetate <10 0.001 to 5 0.01 to 3 Acetaldehyde <5 0.001 to 1 0.005 to 0.5 Water0.1 to 30 1 to 25 5 to 20 C₃+ alcohols <1 0.0001 to 0.5 0.005 to 0.4Second Residue Acetic Acid 0.1 to 45 0.2 to 40 0.5 to 35 Water 45 to 10055 to 99.8 65 to 99.5 Ethyl Acetate <2 <1   <0.5 Ethanol <5 0.001 to 5<2

The remaining water from the second distillate in line 136 may beremoved in further embodiments of the present invention. Depending onthe water concentration, the ethanol product may be derived from thesecond distillate in line 136. Some applications, such as industrialethanol applications, may tolerate water in the ethanol product, whileother applications, such as fuel applications, may require an anhydrousethanol. The amount of water in the distillate of line 136 may be closerto the azeotropic amount of water, e.g., at least 4 wt. %, preferablyless than 20 wt. %, e.g., less than 12 wt. % or less than 7.5 wt. %.Water may be removed from the second distillate in line 136 usingseveral different separation techniques as described herein.Particularly preferred techniques include the use of distillationcolumn, membranes, adsorption units, and combinations thereof.

In one embodiment, any of the residue streams from FIGS. 1 and 2 may beseparated into an acetic acid stream and a water stream when the residuecomprises a majority of acetic acid, e.g., greater than 50 wt. %. Aceticacid may also be recovered in some embodiments from the residue having alower acetic acid concentration. The residue may be separated into theacetic acid and water streams by a distillation column or one or moremembranes. If a membrane or an array of membranes is employed toseparate the acetic acid from the water, the membrane or array ofmembranes may be selected from any suitable acid resistant membrane thatis capable of removing a permeate water stream. The resulting aceticacid stream optionally is returned to the reactor. The resulting waterstream may be directed to a carbonylation system for use as anextractant as discussed above.

In other embodiments, for example, where the second residue comprisesless than 50 wt. % acetic acid, possible options include one or more of:(i) neutralizing the acetic acid, or (ii) reacting the acetic acid withan alcohol. It also may be possible to separate a residue comprisingless than 50 wt. % acetic acid using a weak acid recovery distillationcolumn to which a solvent (optionally acting as an azeotroping agent)may be added. Exemplary solvents that may be suitable for this purposeinclude ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate,vinyl acetate, diisopropyl ether, carbon disulfide, tetrahydrofuran,isopropanol, ethanol, and C₃-C₁₂ alkanes. When neutralizing the aceticacid, it is preferred that the residue comprises less than 10 wt. %acetic acid. Acetic acid may be neutralized with any suitable alkali oralkaline earth metal base, such as sodium hydroxide or potassiumhydroxide. When reacting acetic acid with an alcohol, it is preferredthat the residue comprises less than 50 wt. % acetic acid. The alcoholmay be any suitable alcohol, such as methanol, ethanol, propanol,butanol, or mixtures thereof. The reaction forms an ester that may beintegrated with other systems, such as carbonylation production or anester production process. Preferably, the alcohol comprises ethanol andthe resulting ester comprises ethyl acetate. Optionally, the resultingester may be fed to the hydrogenation reactor.

The columns shown in figures may comprise any distillation columncapable of performing the desired separation and/or purification. Forexample, other than the acid columns describe above, the other columnspreferably are a tray column having from 1 to 150 trays, e.g., from 10to 100 trays, from 20 to 95 trays or from 30 to 75 trays. The trays maybe sieve trays, fixed valve trays, movable valve trays, or any othersuitable design known in the art. In other embodiments, a packed columnmay be used. For packed columns, structured packing or random packingmay be employed. The trays or packing may be arranged in one continuouscolumn or they may be arranged in two or more columns such that thevapor from the first section enters the second section while the liquidfrom the second section enters the first section, etc.

The associated condensers and liquid separation vessels that may beemployed with each of the distillation columns may be of anyconventional design and are simplified in the figures. Heat may besupplied to the base of each column or to a circulating bottom streamthrough a heat exchanger or reboiler. Other types of reboilers, such asinternal reboilers, may also be used. The heat that is provided to thereboilers may be derived from any heat generated during the process thatis integrated with the reboilers or from an external source such asanother heat generating chemical process or a boiler. Although onereactor and one flasher are shown in the figures, additional reactors,flashers, condensers, heating elements, and other components may be usedin various embodiments of the present invention. As will be recognizedby those skilled in the art, various condensers, pumps, compressors,reboilers, drums, valves, connectors, separation vessels, etc., normallyemployed in carrying out chemical processes may also be combined andemployed in the processes of the present invention.

The temperatures and pressures employed in the columns may vary.Temperatures within the various zones will normally range between theboiling points of the composition removed as the distillate and thecomposition removed as the residue. As will be recognized by thoseskilled in the art, the temperature at a given location in an operatingdistillation column is dependent on the composition of the material atthat location and the pressure of column. In addition, feed rates mayvary depending on the size of the production process and, if described,may be generically referred to in terms of feed weight ratios.

In accordance with various embodiments of the present invention, the C₃+alcohols concentration in the finished ethanol composition is controlledwithin the limits for the particular application of the finishedethanol. In certain embodiments, the finished ethanol comprises lessthan 1000 wppm of C₃+ alcohols, e.g., less than 500 wppm or less than400 wppm. For example, the amount of isopropanol in the finished ethanolmay be from 80 to 1,000 wppm, e.g., from 95 to 1,000 wppm, from 100 to700 wppm, or from 150 to 500 wppm. In particular, one or moresidestreams may reduce isopropanol concentrations in distillate thatexceed 1000 wppm. In preferred embodiments, one or more sidestreams arepositioned at a point(s) approximate to where isopropanol, n-propanol,n-butanol, and/or 2-butanol build up within the column.

After using a sidestream to reduce the concentration of C₃+ alcohols,the finished ethanol composition of the present invention preferablycontains very low amounts, e.g., less than 0.5 wt. %, of other alcohols,such as methanol, butanol, isobutanol, isoamyl alcohol and other C₄-C₂₀alcohols. In one embodiment, the amount of isopropanol in the finishedethanol composition is from 80 to 1,000 wppm, e.g., from 95 to 1,000wppm, from 100 to 700 wppm, or from 150 to 500 wppm.

The final ethanol product produced by the processes of the presentinvention may be taken from a stream that primarily comprises ethanolfrom exemplary systems shown in the figures. The ethanol product may bean industrial grade ethanol comprising from 75 to 96 wt. % ethanol,e.g., from 80 to 96 wt. % or from 85 to 96 wt. %, based on the totalweight of the ethanol product. Exemplary finished ethanol compositionalranges are provided below in Table 7.

TABLE 7 FINISHED ETHANOL COMPOSITIONS Component Conc. (wt. %) Conc. (wt.%) Conc. (wt. %) Ethanol 75 to 96 80 to 96 85 to 96 Water <12  1 to 9 3to 8 Acetic Acid <1   <0.1 <0.01 Ethyl Acetate <2   <0.5 <0.05 Acetal <0.05  <0.01  <0.005 Acetone  <0.05  <0.01  <0.005 Isopropanol <0.5<0.1 <0.05 n-propanol <0.5 <0.1 <0.05

In one embodiment, the finished ethanol composition is substantiallyfree of acetaldehyde, optionally comprising less than 8 wppmacetaldehyde, e.g., less than 5 wppm or less than 1 wppm.

In some embodiments, when further water separation is used, the ethanolproduct may be withdrawn as a stream from the water separation unit asdiscussed above. In such embodiments, the ethanol concentration of theethanol product may be higher than indicated in Table 5, and preferablyis greater than 97 wt. % ethanol, e.g., greater than 98 wt. % or greaterthan 99.5 wt. %. The ethanol product in this aspect preferably comprisesless than 3 wt. % water, e.g., less than 2 wt. % or less than 0.5 wt. %.

The finished ethanol composition produced by the embodiments of thepresent invention may be used in a variety of applications includingapplications as fuels, solvents, chemical feedstocks, pharmaceuticalproducts, cleansers, sanitizers, hydrogenation transport or consumption.In fuel applications, the finished ethanol composition may be blendedwith gasoline for motor vehicles such as automobiles, boats and smallpiston engine aircraft. In non-fuel applications, the finished ethanolcomposition may be used as a solvent for toiletry and cosmeticpreparations, detergents, disinfectants, coatings, inks, andpharmaceuticals. The finished ethanol composition may also be used as aprocessing solvent in manufacturing processes for medicinal products,food preparations, dyes, photochemicals and latex processing.

The finished ethanol composition may also be used as a chemicalfeedstock to make other chemicals such as vinegar, ethyl acrylate, ethylacetate, ethylene, glycol ethers, ethylamines, aldehydes, and higheralcohols, especially butanol. In the production of ethyl acetate, thefinished ethanol composition may be esterified with acetic acid. Inanother application, the finished ethanol composition may be dehydratedto produce ethylene. Any known dehydration catalyst can be employed todehydrate ethanol, such as those described in copending U.S. Pub. Nos.2010/0030002 and 2010/0030001, the entireties of which are incorporatedherein by reference. A zeolite catalyst, for example, may be employed asthe dehydration catalyst. Preferably, the zeolite has a pore diameter ofat least about 0.6 nm, and preferred zeolites include dehydrationcatalysts selected from the group consisting of mordenites, ZSM-5, azeolite X and a zeolite Y. Zeolite X is described, for example, in U.S.Pat. No. 2,882,244 and zeolite Yin U.S. Pat. No. 3,130,007, theentireties of which are hereby incorporated herein by reference.

In order that the invention disclosed herein may be more efficientlyunderstood, an example is provided below. It should be understood thatthis example is for illustrative purposes only and is not to beconstrued as limiting the invention in any manner.

Example

The following examples were prepared with ASPEN Plus 7.1 simulationsoftware to test various feed composition and separation systems.

FIGS. 3 and 4 demonstrate bulging of C₃+ alcohols within columns. FIG. 3shows a bulge in a first column of separation system shown in FIG. 1.FIG. 4 shows a bulge in a second column of separation system shown inFIG. 2. To reduce the concentration of C₃+ alcohols, one or moresidestreams may be taken at trays 12 and 23 in FIG. 3, and at tray 10 inFIG. 4.

While the invention has been described in detail, modifications withinthe spirit and scope of the invention will be readily apparent to thoseof skill in the art. In addition, it should be understood that aspectsof the invention and portions of various embodiments and variousfeatures recited herein and/or in the appended claims may be combined orinterchanged either in whole or in part. In the foregoing descriptionsof the various embodiments, those embodiments which refer to anotherembodiment may be appropriately combined with one or more otherembodiments, as will be appreciated by one of skill in the art.Furthermore, those of ordinary skill in the art will appreciate that theforegoing description is by way of example only, and is not intended tolimit the invention.

We claim:
 1. A process for producing ethanol, comprising: hydrogenatingacetic acid in a reactor in the presence of a catalyst to form a crudeethanol product; separating at least a portion of the crude ethanolproduct in a first distillation column to yield a first residuecomprising acetic acid and water, wherein a substantial portion of thewater in the crude ethanol product that is fed to the column is removedin the first residue, a first distillate comprising ethanol, ethylacetate and water, and one or more sidestreams comprising one or moreC₃+ alcohols; removing water from at least a portion of the firstdistillate to yield an ethanol mixture stream comprising less than 10wt. % water; and recovering ethanol from the ethanol mixture stream. 2.The process of claim 1, wherein said one or more C₃+ alcohols areselected from the group consisting of isopropanol, n-propanol,n-butanol, 2-butanol, isobutanol, tert-butanol, 2,2-dimethyl-1-propanol,3-pentanol, 2-pentanol, 1-pentanol, 3-methyl-2-butanol,2-methyl-2-butanol, a mixture thereof, and an azeotrope thereof.
 3. Theprocess of claim 1, wherein said one or more sidestreams comprise one ormore C₃ to C₆ alcohols, a mixture thereof, and an azeotrope thereof. 4.The process of claim 1, wherein the first distillate comprisessubstantially none of said one or more C₃+ alcohols.
 5. The process ofclaim 1, wherein the first distillate comprises less than 1000 wppm ofsaid one of more C₃+ alcohols.
 6. The process of claim 1, wherein wateris removed from the first distillate using an adsorption unit, membrane,extractive column distillation, molecular sieve, or a combinationthereof.
 7. The process of claim 6, wherein the adsorption unit is apressure swing adsorption unit or a thermal swing adsorption unit. 8.The process of claim 1, wherein the ethanol mixture stream comprisesless than 6 wt. % water.
 9. The process of claim 1, further comprisingseparating a portion of the feed to a second distillation column toyield a second residue comprising ethanol and a second distillatecomprising ethyl acetate.
 10. The process of claim 1, wherein the aceticacid is formed from methanol and carbon monoxide, wherein each of themethanol, the carbon monoxide, and hydrogen for the hydrogenating stepis derived from syngas, and wherein the syngas is derived from a carbonsource selected from the group consisting of natural gas, oil,petroleum, coal, biomass, and combinations thereof.
 11. A process forproducing ethanol, comprising: providing a crude ethanol product;separating at least a portion of the crude ethanol product in a firstdistillation column to yield a first residue comprising acetic acid andwater, wherein a substantial portion of the water in the crude ethanolproduct that is fed to the column is removed in the first residue, afirst distillate comprising ethanol, ethyl acetate and water, and one ormore sidestreams comprising one or more C₃+ alcohols; removing waterfrom at least a portion of the first distillate to yield an ethanolmixture stream comprising less than 10 wt. % water; and recoveringethanol from the ethanol mixture stream.
 12. The process of claim 11,wherein said one or more C₃+ alcohols are selected from the groupconsisting of isopropanol, n-propanol, n-butanol, 2-butanol, isobutanol,tert-butanol, 2,2-dimethyl-1-propanol, 3-pentanol, 2-pentanol,1-pentanol, 3-methyl-2-butanol, 2-methyl-2-butanol, a mixture thereof,and an azeotrope thereof.
 13. The process of claim 11, wherein said oneor more sidestreams comprise one or more C₃ to C₆ alcohols, a mixturethereof, and an azeotrope thereof.
 14. The process of claim 11, whereinthe first distillate comprises substantially none of said one or moreC₃+ alcohols.
 15. The process of claim 11, wherein the first distillatecomprises less than 1000 wppm of said one of more C₃+ alcohols.
 16. Theprocess of claim 11, wherein water is removed from the first distillateusing an adsorption unit, membrane, extractive column distillation,molecular sieve, or a combination thereof.
 17. The process of claim 16,wherein the adsorption unit is a pressure swing adsorption unit or athermal swing adsorption unit.
 18. The process of claim 11, wherein theethanol mixture stream comprises less than 6 wt. % water.
 19. Theprocess of claim 11, further comprising separating a portion of the feedto a second distillation column to yield a second residue comprisingethanol and a second distillate comprising ethyl acetate.
 20. Theprocess of claim 11, wherein said one or more C₃+ alcohols are selectedfrom the group consisting of isopropanol, n-propanol, n-butanol, and2-butanol.